All in all we thus have a group of a dozen new types, springing from an original form in one restricted locality, and seen to grow there, or arising in the garden from seeds collected from the original locality. Without any doubt the germs of the new types are fully developed within the seed, ready to be evolved at the time of germination. More favorable conditions in the field would no doubt allow all of the described new species to unfold their attributes there, and to come into competition with each other and with the common parents. But obviously this is only of secondary importance, and has no influence on the fact that a number of new types, analogous to the older swarms of _Draba_, _Viola_ and of many other polymorphous species, have been seen to arise directly in the wild state.

[547]

LECTURE XIX

EXPERIMENTAL PEDIGREE-CULTURES

The observation of the production of mutants in the field at Hilversum, and the subsequent cultivation of the new types in the garden at Amsterdam, gives ample proof of the mutability of plants. Furthermore it furnishes an analogy with the hypothetical origin of the swarms of species of _Draba_ and _Viola_. Last but not least important it affords material for a complete systematic and morphologic study of the newly arisen group of forms.

The physiologic laws, however, which govern this process are only very imperfectly revealed by such a study. The instances are too few. Moreover the seeds from which the mutants spring, escape observation. It is simply impossible to tell from which individual plants they have been derived. The laevifolia and the brevistylis have been found almost every year, the first always recurring on the same spot, the second on various parts of the original field. It is therefore allowable to assume a common [548] origin for all the observed individuals of either strain. But whether, besides this, similar strains are produced anew by the old _lamarckiana_ group, it is impossible to decide on the sole ground of these field-observations.

The same holds good with the other novelties. Even if one of them should germinate repeatedly, without ever opening its flowers, the possibility could not be excluded that the seeds might have come originally from the same capsule but lain dormant in the earth during periods of unequal length.

Other objections might be cited that can only be met by direct and fully controlled experiments. Next to the native locality comes the experimental garden. Here the rule prevails that every plant must be fertilized with pollen of its own, or with pollen of other individuals of known and recorded origin. The visits of insects must be guarded against, and no seeds should be saved from flowers which have been allowed to open without this precaution. Then the seeds of each individual must be saved and sown separately, so as to admit of an appreciation, and if necessary, a numerical determination of the nature of its progeny. And last but not least the experiments should be conducted in a similar manner during a series of successive years.